This invention relates to a receiving material with a glossy surface for ink-jet printing. The ink-jet process involves the transference of droplets of an ink-like liquid onto a receiving material by various means. One of the processes is the Hertz process which allows minute droplets of ink, fired through special jets and controlled by digital electronics to produce images of very high definition directly from electronic data.
As ink-jet printing is improved functionally, the demands placed upon the receiving material increase. A picture produced by the ink-jet process should show:
high definition PA0 high color density PA0 an adequate number of color shades/tones PA0 good smudge resistance. PA0 The receiving material must absorb the ink as quickly as possible. PA0 The ink droplets must: PA0 Ink diffusion in the receiving material must not be too high in order to increase the diameter of the droplets only as much as is absolutely necessary. PA0 The receiving material must present a glossy surface to achieve a high reflection density and a high degree of color brilliance.
In order to achieve this the following basic requirements must be met:
be sprayed onto the receiving material as exactly as possible in a circular shape, and PA1 diffuse slightly and evenly up to a fixed limit.
Some requirements pose contradictions, i.e. if smudging resistance is acquired too quickly the droplets cannot diffuse correctly and a distinct disadvantage to the clarity of the image created.
With the invention claims for the receiving material in view, it is our object to find a way to achieve an image whose color density and smudge resistance are as high as possible.
A receiving material for multicolored ink-jet printing generally consists of a support material coated with an ink receiving layer. Support materials may be foils of polyester resin, diacetate resin or paper and other materials. The ink receiving layers fundamentally consist of a mixture of pigment/binding agent.
As well as increasing the degree of whiteness of the material, the pigments serve to retain the dyes of the ink in the material surface. A high pigment concentration leads to a high degree of porosity of the layer (DE-PS 30 24 205). This produces desirable smudge resistance standards, but at the same time the pigments penetrate into the inner image receiving materials and this, in turn, worsens the color density of the image.
The application of gelatin coated paper for ink-jet receiving materials is already known (DE-PS 22 34 823). The gelatin is to improve smudge resistance and increase definition qualities. The greatest disadvantage of this receiving material is that the droplets sprayed on to create the image do not become acceptably smudge resistant within the time desired, but only after approximately 10 seconds. A further disadvantage is that the droplets do not run either sufficiently or quickly enough.
The Patent Specification DE-OS 30 167 66 describes a receiving material consisting of a base paper, internally sized to create a defined degree of water absorption, coated with a water soluble polymer. This, it is claimed, produces a printed image of high definition and color density. A disadvantage of this receiving material is the fact that in order to achieve the desired color density, the material must be smoothed in a separate work process after the ink receiving layer has been applied, i.e. by means of a gloss or super calender.
Japanese Patent Specification JP 58-193 185 describes how two coatings are applied to a single support material. The top layer consisting of polyvinyl alcohol ensures good smudge resistance, i.e. quick ink absorption. The bottom layer containing synthetic silicic acid is to ensure high color density. A disadvantage of this receiving material is the unsatisfactory color density, as well as the need for two work processes, i.e. two layers must be applied separately and must finally be smoothed by means of a calender.
It is therefore the object of the present invention to produce a receiving material for the ink-jet process which is not subject to the above listed disadvantages and which distinguishes itself especially by high color density of the printed image in conjunction with a quickly achieved smudge resistance of the ink sprayed.
A further object of the invention is that the receiving material so produced has a glossy surface achieved by as few work processes as possible, wording the necessity for additional smoothing processes.
These objects are achieved by using a polyolefin coated base paper onto which an ink receiving layer has been applied which contains a mixture of gelatin and starch (of a grain size less than 20 .mu.m). The starch is either rice and/or wheat starch, type B. The quantity ratio is preferably between 1:1 and 10:1. One of the forms preferred for the ink receiving layer contains additionally a copolymer containing polar groups such as an acrylate copolymer containing carboxyl groups, metal combined carboxyl groups and/or nitrile groups or a carboxylized vinylidene copolymer among others.
In another preferred form, the quantity of copolymer containing polar groups in the mixture is between 0.5% weight and 35% weight with a preferred quantity of between 4 and 10% weight.
The ink receiving layer may contain all the other usual additives, such as organic or inorganic pigments (polymethylmethacrylate, polystyrene, carbamide formaldehyde resins, silica, CaCO.sub.3, TiO.sub.2, BaSO.sub.4, etc.), hardeners (chrome alum, TAF/formaldehyde), wetting agents (i.e. saponin), shading dyestuffs, antistatic agents and other auxiliary agents.
The coating weights of the ink receiving layer are between 0.5 and 10 g/m.sup.2, preferably between 2 and 7 g/m.sup.2. The ink receiving coating mass may be applied to the support material by any of the usual coating and metering processes, such as roll coating, nip coating and engraving, as well as air brushing or blade knife metering.
The polyolefin used in the coating of the base paper should preferably be of the low density polyethylene (LDPE) and/or high density polyethylene (HDPE). However, other polyolefins, such as LLDPE or polypropylene may be utilized. The coating weight of this polyolefin layer, in which other additives may be included, should be at least 5 g/m.sup.2.
It was surprising that a combination of binding agents in the mixture, i.e. a mixture of at least gelatin and starch, should produce such excellent printed image quality as the single components did not produce correspondingly good results.
The gloss surface of the receiving material according to the invention needs no additional treatment whatsoever, either by means of a gloss calender or any other means, and is obviously achieved by a mutual effect of the polyethylene coated base paper and the ink receiving layer.
Surprisingly, the very good results regarding color density are also achieved without pigmenting the ink receiving layer.
Moreover, the material shows good water resistance qualities as well as good abrasive resistance of the printed image.